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Three-dimensional numerical calculation was performed to investigate the effects of partial blockage inside cylindrical film holes on the film cooling effectiveness over a flat plate. Five blockage ratios ranged from 0.1 to 0.5 and a series of blockage positions were considered under the blowing ratios of 0.3–1.5. It is found that the blockage position has a significant influence on mainstream-coolant jet interaction. The partial blockage located at the leading edge of coolant-hole exit mitigates the primary vortices due to mainstream-coolant jet interaction. The coolant jet penetration along vertical direction is suppressed and the peak velocity along streamwise direction is augmented under the action of partial blockage at the upstream side of film holes, providing an increment of film cooling effectiveness, especially under high blowing ratio. While the partial blockages located at the trailing or lateral edges of coolant-hole exit weaken the film cooling effectiveness. In relation to the partial blockage located in the vicinity of coolant-hole exit, the partial blockage located in the vicinity of coolant-hole inlet or middle has less impaction on the film cooling effectiveness under low blowing ratio.

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